The following invention relates to a flat panel matrix-addressed display of the type that utilizes orthogonally disposed sets of electrodes sandwiching an electroluminescent medium and provides an electrode configuration for minimizing the effective contact density of the electrodes at the edges of the panel. This allows a higher resolution flat panel display to be served by a lower effective density of interconnects.
Matrix addressed luminescent displays such as thin-film electroluminescent (TFEL) displays include sets of parallel elongate electrodes deposited on a substrate which sandwich a laminate, which includes an electroluminescent phosphor layer, between two dielectric layers. The electrodes include a front transparent set of electrodes deposited on a substrate and a rear set of electrodes oriented perpendicular to the front set. This is a matrix addressable display where the matrix consists of pixel points located at the field-of-view intersections of the front and rear electrode sets. In order to create the electric fields necessary to cause luminescence at these pixel points, the electrodes are connected to driving electronics at contact points along the periphery of the panel.
High resolution panels having a large number of pixel points require a correspondingly large number of electrodes. This in turn leads to very high contact densities along the sides of the display for interconnection to the driving electronics. For example a conventional electrode configuration for flat panel display is shown in FIG. 1, where each matrix display line (for either row or column electrodes) is extended outwardly to the periphery of the panel for electrical connection. This single row of contact pads may be too crowded to accommodate the tolerances available in connectors which are designed to connect these contact pads to the driving electronics.
An alternative type of electrode configuration which has been used in the past is shown in FIG. 2. In this configuration, an interdigitated layout is used. Adjacent lines have contacts at opposite sides of the display in an alternating fashion, which effectively reduces the contact density to half of that of FIG. 1. This may not be practical, however, for some drive schemes, particularly those used with TFEL panels, because the driving electronics may need to connect to all lines at one end of the panel. In these cases one possible solution, which is shown in FIG. 3, is to fan out the ends of the electrodes toward the edge of the panel in order to provide more room between termination points. This, however, requires a larger border area which may be inconsistent with design goals regarding the size of the panel and the area needed for the visual display.
In some cases it may be possible to reduce the contact density by arranging the contacts for adjacent display lines to be staggered into N rows. This type of layout is shown in FIG. 4. For example if N=2 the contact pads in the outer row connect to every other display line, and pads in the inner row connect to the remaining alternate display lines. The conducting leads routed to the outer row of contact pads pass in between the pads of the inner row of contacts. If these leads are narrower than the inner row pad separations, the inner and outer row pads may have a pitch (center to center distance) that is twice that of the display lines without fanning. This may result in a net reduction in connection difficulty for some connectors, particularly matched one-on-one types. However, the inner row will still have as many conductors as there are display lines, so there is no real reduction in number density. In high resolution panels which require a large number of lines per unit area, this may limit the acceptable tolerances for connectors to driving electronics.
The means used for connecting the contact pads to the driving electronics must do so without forming short-circuits between adjacent contact pads. When conductors occupy the space between adjacent pads, the tolerance for misalignment is substantially reduced. This is a potential problem with the staggered row approach shown in FIG. 4 using conventional conductor-on-elastomer unaligned or random interconnects. These are conductor-on-elastomer connectors which have a higher resolution than the pads being interconnected so that only the two mating sets of pads being interconnected require alignment. The connectors in between are not aligned to either set. However, for high contact densities, the chances for forming a short-circuit are substantial with the staggered geometry of FIG. 4. Even with a one-on-one type of connector there must be careful alignment or an overhanging portion may short to any conductors routed near the pads.